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 Title: HIGH PRECISION 2.0 μm PHOTOACOUSTIC SPECTROMETER FOR DETERMINATION OF THE 13CO2/12CO2 ISOTOPE RATIO Author(s): Reed, Zachary Contributor(s): Hodges, Joseph T. Subject(s): Instrument/Technique Demonstration Abstract: We have developed a portable photoacoustic spectrometer for high precision measurements of the $^{13}$CO$_{2}$/$^{12}$CO$_{2}$ isotope ratio and the absolute molar concentration of each isotope. The spectrometer extends on our previous work at 1.57 $mu$m [1], and now employs two separate intensity modulated distributed feedback lasers and a fiber amplifier, operating in the 2.0 $mu$m wavelength region. Each DFB is selected to probe individual spectrally isolated ro-vibrational transitions for $^{12}$CO$_{2}$ and $^{13}$CO$_{2}$. The spectrometer is actively temperature controlled, mitigating variations in the two spectral line intensities and the temperature dependent system response. _x000d_ _x000d_ For measurements of ambient concentrations of carbon dioxide at nominally natural abundance in dry air, we demonstrate a measurement precision of 140 ppb for $^{12}$CO$_{2}$ with a 1 s averaging time and 10 ppb for $^{13}$CO$_{2}$ with a 60 s averaging time. Precision in $delta$13C of better than 0.1 permil is demonstrated. The analyzer response is calibrated in terms of certified gas mixtures and compared to characterization by cavity ringdown spectroscopy. We also investigate how water vapor affects the photoacoustic signals by promoting collisional relaxation for each isotope. _x000d_ _x000d_ [1] Z.D. Reed, B. Sperling, et al. App. Phys. B. 117, 645-657, 2014 Issue Date: 6/19/2017 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/97192 DOI: 10.15278/isms.2017.MK07 Date Available in IDEALS: 2017-07-272018-01-29
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